"We are the richest people on average in the world's history," says Richard Scylla, an economic historian.
Scylla has run the numbers, and here are his results: The U.S. today is richer than the Roman Empire when it ruled much of the Old World and richer than the British Empire when it ruled much of the New World.
But when the sun never set on the British Empire, how rich were they compared to us?
"They were probably, I would say, about one-tenth to one-fifth as rich as we are," Scylla says.
What makes this economy so strong isn't big factories, but big ideas. Smokestacks have been replaced by microchips. For example, Bill Gates, had an idea to make computers work easily and became one of the richest men in history.
And the wealth is spreading. Consumers are watching Wall Street go up and they feel rich. Which means they buy more things - such as cars and jewelry - which boosts the economy and starts the cycle all over again.
However, Scylla says, "These things don't go on forever."
History teaches us about good times and bad. Everyone who remembers the celebration when the market hit 1,000 in President Richard Nixon's day also remembers it fell steadily for the next year and a half.
"There's no reason we couldn't fall 35 percent in the next 18 months," Scylla says. "We've seen it before. It could easily happen again. And it always happens when you hit new highs and everybody's optimistic."
So it might be wise for investors to remember - as they pat themselves on the back - to always look over their shoulder.
Reported By Richard Schlesinger